Unraveling mechanisms for expert object recognition: Bridging brain activity and behavior.

Behavioral sensitivity to object transformations and the response to novel objects (Greebles) in the fusiform face area (FFA) was measured several times during expertise training. Sensitivity to 3 transformations increased with expertise: (a) configural changes in which halves of objects were misaligned, (b) configural changes in which some of the object parts were moved, and (c) the substitution of an object part with a part from a different object. The authors found that holistic-configural effects can arise from object representations that are differentiated in terms of features or parts. Moreover, a holistic-inclusive effect was correlated with changes in the right FFA. Face recognition may not be unique in its reliance on holistic processing, measured in terms of both behavior and brain activation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Implicit learning in 3D object recognition: the importance of temporal context

A novel architecture and set of learning rules for cortical self-organization is proposed. The model is based on the idea that multiple information channels can modulate one another's plasticity. Features learned from bottom-up information sources can thus be influenced by those learned from contextual pathways, and vice versa. A maximum likelihood cost function allows this scheme to be implemented in a biologically feasible, hierarchical neural circuit. In simulations of the model, we first demonstrate the utility of temporal context in modulating plasticity. The model learns a representation that categorizes people's faces according to identity, independent of viewpoint, by taking advantage of the temporal continuity in image sequences. In a second set of simulations, we add plasticity to the contextual stream and explore variations in the architecture. In this case, the model learns a two-tiered representation, starting with a coarse view-based clustering and proceeding to a finer clustering of more specific stimulus features. This model provides a tenable account of how people may perform 3D object recognition in a hierarchical, bottom-up fashion.     

Are edges sufficient for object recognition?

The authors argue that the concept of "edges" as used in current research on object recognition obscures the significant difficulties involved in interpreting stimulus information. Edges have sometimes been operationalized as line drawings, which can be an invalid and misleading practice. A new method for evaluating the utility of edge information, operationalized as the outputs of a local, signal-based edge extractor, is introduced. With 1-s exposures, the accuracy of identifying objects in the edge images was found to be less than half that with color photographs. Therefore, edges are far from being sufficient for object recognition. Alternative approaches to the problem of interpreting stimulus information are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociation of object recognition and spatial localization abilities following temporal lobe lesions in humans.

Discrete extrastriate cortical visual systems in nonhuman primates consisting of an occipitotemporal object recognition system and an occipitoparietal spatial localization system have been proposed. Patients undergoing left (n?=?81) or right (n?=?77) anterior temporal lobectomy were administered tests of object recognition (facial recognition) and spatial localization (line orientation) preoperatively and 6 mo postoperatively to determine the effects on the what and where visual systems. Postoperatively there was dissociation in performance with significant loss in facial recognition ability and concomitant improvement in line orientation performance. The pattern of performance was similar for both groups. The findings suggest that anterior temporal lobectomy had a specific effect on the occipitotemporal object recognition system while leaving the occipitoparietal spatial localization system unaffected. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Coordinate frame for symmetry detection and object recognition.

Ss were required to determine whether dot patterns were symmetric. Cuing the Ss in advance about the orientation of the axis of symmetry produced a substantial speedup in performance (Exps 1 and 3) and an increase in accuracy with brief displays (Exp 2). The effects appeared roughly additive, with an overall advantage for vertical symmetry; thus, the vertical axis effect is not due to a tendency to prepare for the vertical axis. The cuing advantage was found to depend upon the S's knowing in advance the spatial location as well as orientation of the frame of reference (Exp 4). Exp 5 provided evidence that the frame of reference responsible for these effects is the same as the one that determines shape perception: Ss viewed displays containing a letter (at an unpredictable orientation) and a dot pattern, rapidly naming the letter and then determining whether the dots were symmetric about a prespecific axis. When the top–bottom axis of the letter was oriented the same way as the axis of symmetry for the dots, symmetry judgments were significantly more accurate. Results suggest a single frame of reference for both types of judgment. A theory of visual symmetry is proposed to account for the phenomena and characterize their relation to "mental rotation" effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Coordinate transformations in object recognition.

A basic problem of visual perception is how human beings recognize objects after spatial transformations. Three central classes of findings have to be accounted for: (a) Recognition performance varies systematically with orientation, size, and position; (b) recognition latencies are sequentially additive, suggesting analogue transformation processes; and (c) orientation and size congruency effects indicate that recognition involves the adjustment of a reference frame. All 3 classes of findings can be explained by a transformational framework of recognition: Recognition is achieved by an analogue transformation of a perceptual coordinate system that aligns memory and input representations. Coordinate transformations can be implemented neurocomputationally by gain (amplitude) modulation and may be regarded as a general processing principle of the visual cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scenario recognition for temporal reasoning in medical domains

The recognition of high level clinical scenes is fundamental in patient monitoring. In this paper, we propose a technique for recognizing a session, i.e. the clinical process evolution, by comparison against a predetermined set of scenarios, i.e. the possible behaviors for this process. We use temporal constraint networks to represent both scenario and session. Specific operations on networks are then applied to perform the recognition task. An index of temporal proximity is introduced to quantify the degree of matching between two temporal networks in order to select the best scenario fitting a session. We explore the application of our technique, implemented in the Déjà Vu system, to the recognition of typical medical scenarios with both precise and imprecise temporal information.     

2D observers for human 3D object recognition?

In human object recognition, converging evidence has shown that subjects' performance depends on their familiarity with an object's appearance. The extent of such dependence is a function of the inter-object similarity. The more similar the objects are, the stronger this dependence will be and the more dominant the two-dimensional (2D) image-based information will be. However, the degree to which three-dimensional (3D) model-based information is used remains an area of strong debate. Previously the authors showed that all models with independent 2D templates that allowed 2D rotations in the image plane cannot account for human performance in discriminating novel object views. Here the authors derive an analytic formulation of a Bayesian model that gives rise to the best possible performance under 2D affine transformations and demonstrate that this model cannot account for human performance in 3D object discrimination. Relative to this model, human statistical efficiency is higher for novel views than for learned views, suggesting that human observers have used some 3D structural information.     

Effects of outline shape in object recognition.

The use of outline shape in recognizing objects was investigated in 4 experiments. In Experiment 1, participants matched a shaded image to either another shaded image or a silhouette. In Experiment 2, they initially named shaded images; later they named either shaded images or silhouettes. Performance in both experiments was predicted by changes in the outline shape of the stimuli. The same matching (Experiment 3) and priming (Experiment 4) paradigms were then used to investigate recognition with objects that were rotated between presentations so as to change the outline shape of the object. Recognition was predicted by changes to outline shape. These results place constraints on models of object recognition and are most compatible with viewpoint-dependent models of recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Training 'greeble' experts: a framework for studying expert object recognition processes

Twelve participants were trained to be experts at identifying a set of 'Greebles', novel objects that, like faces, all share a common spatial configuration. Tests comparing expert with novice performance revealed: (1) a surprising mix of generalizability and specificity in expert object recognition processes; and (2) that expertise is a multi-faceted phenomenon, neither adequately described by a single term nor adequately assessed by a single task. Greeble recognition by a simple neural-network model is also evaluated, and the model is found to account surprisingly well for both generalization and individuation using a single set of processes and representations.     

Pyrithiamine-induced thiamine deficiency impairs object recognition in rats.

Pyrithiamine-induced thiamine deficiency (PTD) in rats is used to model the etiology, diencephalic neuropathology, and memory deficits of Korsakoff's amnesia. We assessed the performance of rats exposed to PTD on a test of object recognition—nonrecurring-items delayed nonmatching-to-sample (DNMS). PTD produced thalamic lesions similar to those of Korsakoff's amnesics and similar to those previously observed in PTD rats. PTD rats required more trials to master DNMS at a 4-sec retention delay than did controls, and after they had done so, they performed more poorly than controls at delays of 15, 30, 60, and 120 sec. DNMS deficits were also observed in PTD rats that received training prior to PTD treatment. These findings support the validity of the PTD rat model of Korsakoff's disease by demonstrating that PTD rats display object-recognition deficits that are similar to those reported in Korsakoff amnesics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of perceptual load in object recognition.

Predictions from perceptual load theory (Lavie, 1995, 2005) regarding object recognition across the same or different viewpoints were tested. Results showed that high perceptual load reduces distracter recognition levels despite always presenting distracter objects from the same view. They also showed that the levels of distracter recognition were unaffected by a change in the distracter object view under conditions of low perceptual load. These results were found both with repetition priming measures of distracter recognition and with performance on a surprise recognition memory test. The results support load theory proposals that distracter recognition critically depends on the level of perceptual load. The implications for the role of attention in object recognition theories are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rhinal cortex lesions and object recognition in rats.

Tested 11 male rats with bilateral lesions of lateral entorhinal cortex and perirhinal cortex on a nonrecurring-items delayed nonmatching-to-sample (DNMS) task resembling the one that is commonly used to study object recognition (OR) in monkeys. The rats were tested at retention delays of 4, 15, 60, 120, and 600 sec before and after surgery. After surgery, they displayed a delay-dependent deficit: They performed normally at the 4-sec delay but were impaired at delays of 15 sec or longer. The addition of bilateral amygdala lesions did not increase their DNMS deficits. The present finding of a severe DNMS deficit following rhinal cortex damage is consistent with the authors' previous finding that bilateral lesions of the hippocampus cause only mild DNMS deficits in rats unless there is also damage to rhinal cortex (D. G. Mumby et al, 1992). These findings add to accumulating evidence that the rhinal cortex, but not the amygdala, plays a critical role in OR. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Three-dimensional object recognition based on the combination of views

Visual object recognition is complicated by the fact that the same 3D object can give rise to a large variety of projected images that depend on the viewing conditions, such as viewing direction, distance, and illumination. This paper describes a computational approach that uses combinations of a small number of object views to deal with the effects of viewing direction. The first part of the paper is an overview of the approach based on previous work. It is then shown that, in agreement with psychophysical evidence, the view-combination approach can use views of different class members rather than multiple views of a single object, to obtain class-based generalization. A number of extensions to the basic scheme are considered, including the use of non-linear combinations, using 3D versus 2D information, and the role of coarse classification on the way to precise identification. Finally, psychophysical and biological aspects of the view-combination approach are discussed. Compared with approaches that treat object recognition as a symbolic high-level activity, in the view-combination approach the emphasis is on processes that are simpler and pictorial in nature.     

State-dependent impairment in object recognition after hippocampal NOS inhibition

In the present study we investigated the consequences of hippocampal nitric oxide synthase (NOS) inhibition on the performance in an object recognition task in rats. In a first study we injected Nomega-nitro-L-arginine (L-NA) into the hippocampus directly after the first trial. One hour later the discrimination performance of the animals was assessed. It was found that 10 microg and 30 microg, but not 3 microg, L-NA impaired the performance of the rats. In a second study in which we injected L-NA 45 min before the first trial no effects of treatment (10 microg and 30 microg) were observed. Since treatment with 30 microg has been found to inhibit hippocampal NOS almost completely and lasts longer than 2 h, it was concluded that hippocampal NOS inhibition induced a state-dependent performance deficit. Consequently, studies that examine the effects of NOS inhibition on cognitive functions should take this confounding effect into account.     

Spatio-temporal influences at the neural level of object recognition

In late 1988, Miyashita published work reporting recordings of single cells in the inferotemporal cortex of the macaque monkey (Miyashita 1988 Nature 335 817-20). He described the responses of neurons to a sequence of random fractal pattern images, and how many of the neurons tested were seen to respond strongly to a subset of the images on the basis of sequence presentation order, i.e. appearance in time, rather than their spatial similarity. In this work, I describe a local Hebb-like learning rule which in conjunction with a simple feedforward neural architecture is capable of replicating the type of temporal-order association apparent in the cells from which he made recordings. The paper also advances reasons for requiring such learning by describing its possible role in establishing transformation invariant representations of objects.